I. Field of the Invention
The present invention is directed generally to implantable body organ stimulators and, more specifically, to a system for connecting electrical lead to implanted electrical stimulus generating devices without having to access these connections directly with tools, or the like, to effect the connection or disconnection.
II. Description of the Related Art
Certain particularly useful medical treatment systems involve devices chronically implanted in the body that deliver pulses of electrical energy to stimulate or otherwise affect proximate body tissue. An exemplary device of this type, and one which is probably the best known, is the cardiac pacer which includes a pulse generator having a power source and electrical circuitry for generating timed electric pulses to stimulate designated heart muscles. The pulses are delivered through electrically conductive leads having proximal end terminals connected to the pulse generator and one or more unipolar or bipolar distal end electrodes secured to the myocardial tissue at the situs of interest for stimulation at a location remote from the pulse generator itself.
The defibrillator is a further example of a more recent implantable stimulating device. That system is designed to terminate arrhythmias such as ventricular fibrillation or tachycardia, by application of one or more properly timed electrical pulses to the appropriate part of the heart. The defibrillator differs from the pacer in that the electrical pulses involved are of much greater intensity and are delivered only in response to sensing arrhythmias or abnormalities of a certain degree. Other devices, e.g., neuromuscular stimulators, also involve implantable means for delivering electrical impulses through leads from a pulse generator through leads to stimulate tissue.
With respect to such devices, generally, the term "pulse generator" refers to the implantable electronic source device which controls and generates the stimulus, while the term "lead" refers to the insulated conductive wire (or wires) which are electrically and mechanically coupled to the pulse generator and which receive each stimulating impulse from the pulse generator and transmit each impulse to the heart or organ of interest. The lead incorporates at least one electrode which is the conductive element or contact normally exposed or adjacent the distal end of the lead to establish electrical contact with the tissue of interest, such as the heart muscle.
In the case of an implantable cardiac pacer system, either endocardial leads or myocardial leads may be employed. Endocardial leads are internal leads to the heart which enter the heart through a vein and make contact with the endocardium while myocardial leads are those which are attached to the external surface of the heart having an electrode making contact with the myocardium. Established surgical procedures developed and perfected over time are employed for the lead placement with respect to the tissue. These procedures are well known in the art and need not be further treated here. Following placement of lead electrodes, thresholds are determined. Upon indication of satisfactory thresholds, the proximal leads are connected to the pulse generator which is also chronically implanted at a distance from the heart.
The connection of the electrode lead or lead assemblies to the pulse generator has traditionally been accomplished by the insertion of the exposed terminal pin of the lead into a connector block located in a housing attached to but separate from the main chamber of the pulse generator. Inasmuch as the terminal pin and the connector block have exposed conductive surfaces, it also has been necessary for the zone surrounding the terminal pin-connector block to be sealed and maintained free of body fluids. Leakage of body fluids into the cavity or zone occupied by the terminal pin-connector block combination may adversely affect pacer performance. Thus, the system requires a fluid-tight housing and a connection which preserves electrical integrity.
The procedure for inserting the leads into the pulse generator must be one which can be accomplished with a maximum degree of freedom to avoid inadvertent moving of the placed electrode and lead. Of course, in turn, this requires that the procedure for inserting the terminal pin and securing connection of the lead assembly into the connector block be accomplished as easily as possible.
Normally, the lead is generally cylindrical and may have one or more additional sequential axial segments of increasing diameter. The assembly may have a tip (or pin) terminal or both a pin and a ring terminal accessible on that portion of the lead which is received within the connector housing on the body of the pulse generator. The lead connector is durable and rigid and the terminals are axially spaced inward from a seal between the connector housing of the pulse generator and the environment.
Heretofore, the terminal pins have been inserted into a connector block integral with the body of the connector housing and held in place utilizing set screws. Manipulation of a set screw requires that a tool be inserted from outside the body to address the subcutaneously located pulse generator body at a location spaced from the insertion opening in the connector housing in order to accomplish the tightening of the set screw in the connector block to secure the terminal pin in place. A resilient sealing plug is normally installed over the set screw to effect a fluid tight, electrically insulating seal.
Such known means for connecting leads to body implantable devices are exemplified by U.S. Pat. No. 4,461,194 to Moore, in which the seal plug is positioned between the set screw and a cap; U.S. Pat. No. 4,072,154 to Anderson, et al. utilizes a seal plug in conjunction with a set screw to positively retain the lead. Many other similar techniques are used for such devices, all of which require rather traumatic surgical procedures to accomplish any connection or disconnection of the leads to the body of the pulse generator.
In addition, all of these connection techniques require specialized tools which, as a practical matter, are easily misplaced as they are relatively small and not often used; and they are difficult to maintain in a sterile condition. The small parts, such as plugs and set screws, can also easily be misplaced, even within surgical openings in patients.
From the above, it is evident that there has been a continuing need for a simpler approach to connecting and disconnecting the proximal leads of such devices through the connector housing on the body of the pulse generator. Such an approach would eliminate the need for separate small parts and specialized tools. Accordingly, it is a primary object of the present invention to accomplish the connection and disconnection of the proximal ends of subcutaneous electrode lead assemblies of electrically stimulating implanted electrodes to the implanted body of a pulse generator without additional parts or specialty tools.
Another object of the present invention is to connect and disconnect the proximal ends of such leads with minimal need for surgically invasive procedure.
A still further object of the present invention is to accomplish the connecting and disconnecting of the proximal lead assembly ends of in a manner which, though tool-less, is simple, and easy, and which provides a positive and reliable connection.